I hope what I am about to say reads better than how its swirling in my mind!!
I have been reading through the theories that this was an opportunistic crime, evil colliding with good etc. For this theory to work, in my head anyway, there are way too many variables that would not have been present that day. The 12th of September last year was a Friday. Not a day you would expect to find children playing freely in their yards either front or back. Most children targeted by a pedo would be in school or daycare. If it was a weekend then perhaps it would make more sense that someone was waiting for an opportunity to snatch a child.
From what I can understand (and please correct me if I am wrong) but Benaroon drive doesn't seem like a hive of children's activity. Surely if it was opportunistic even a pedo would be smart enough to target an area that has a higher percentage of a child being present to commit a kidnapping and therefore increasing the chance of feeding the addiction.
To me this was calculated, planned and executed with precision. Opportunistic crimes are often sloppy and un-organised resulting in clues being left etc. To the naked eye, there are absolutely zero clues or evidence to move forward with. Obviously the police working this case are privy to far more details then we will ever be and rightly so.
Considering what I think, my opinion is that whomever is responsible for taking William is someone who knew he was going to be there, whether they were told directly or indirectly. Perhaps the only opportunistic part of this, is that G/ma needed her washing machine fixed.....